The statements in this section merely provide background information related to the present disclosure and may or may not constitute prior art.
Increasingly stringent emissions standards continue to present challenges for automobile and motor vehicle engineers and designers throughout the world. For example, new Euro 6d and China 6 particulate emission limits reduced previous particulate number (PN) limits by a factor of ten. This new standard is 6×1011 particles per kilometer.
While port fuel injected (PFI) gasoline engines can generally meet this standard, the industry is increasingly moving to gasoline direct injected (GDI) engines for which such limits represent a significant challenge.
One of the currently accepted solutions to bringing gasoline direct injected engines into conformance with the Euro 6d and China 6 particulate emission limits envisions the use of a gasoline particulate filter (GPF). As the name suggests, in its most basic configuration, a gasoline particulate filter is simply a filter disposed in the exhaust system of the gasoline fueled engine in which particulate matter is trapped and accumulates.
Because any such particulate filter will be of finite size and thus capable of collecting and retaining only a finite amount of particulate matter from the exhaust of the internal combustion engine, the question rather quickly arises of how the filter is purged or regenerated.
It has been determined that a certain amount of oxygen in the exhaust will purge or regenerate the filter if it is at a sufficiently high temperature. Because gasoline internal combustion engines ideally operate at (or very near) a stoichiometric ratio, there is typically little, if any, oxygen in the exhaust during normal, at least partially loaded, operation. However, passive regeneration is possible during fuel cutoff when the amount of oxygen in the exhaust increases, which occurs during a vehicle coast down, but, again, only if it is at a sufficiently high temperature. Accordingly, if the vehicle is utilized for very short trips or operated for short trips in cold weather, the exhaust system and specifically the particulate filter may not reach a passive, self-regenerating temperature, precluding such regeneration.